It is known that the ore which for the major part comprises metal oxides (being various ones, even in the case of iron) must be subjected to a reduction procedure before the metal can be obtained. That reduction operation is effected by means of carbon and possibly hydrogen--or also compounds thereof--which are contained in a reducing gas which is caused to act on the metal ore.
The reduced metal ore then passes into a smelting procedure. In that case, the gas required for the reduction operation is obtained in the region of the reducing and smelting procedure itself, by carbon-bearing substances (for example coke, coal, oil, natural gas) being added to the zone of the metal which has already been reduced and heated, whereby, with the addition of oxygen (in the air), they are broken up or converted in carbon-bearing gas which is fed to the preceding reduction operation.
The conventional blast furnace process is known in that respect, in which both reduction of the metal ore and also formation of the reducing gas as well as subsequent smelting liquifaction of the metal occur in the blast furnace--progressively in a downward direction. In that blast furnace process, among additive substances, coke is possibly mixed with the iron ore, as a carbon carrier. It is known for oil or carbon also to be injected by way of lances into the air flow in the region of the hearth of the blast furnace for better control of the blast furnace process and to save on coke, the consumption of coke thereby also being reduced. This material (oil or coal dust) which is additionally injected must be introduced in very finely distributed form in order to ensure clean adequate gasification. Two articles in the journal "Stahl and Eisen", No 4 of Feb. 25, 1985, pages 211-220 contain summaries relating to the injection of coal dust into blast furnaces. The injection of coal dust was forced upon operators in particular in the course of rising oil prices. In that respect it was found that when adopting the injection procedure, because of the short time available of about 10 ms, good results, more specifically almost complete gasification of the coal dust, were achieved only with grain sizes of below 0.1 mm., even if tests were also successfully carried out with some installations, using larger grain sizes.
It has also already been proposed that, instead of injecting oil and coal dust, other carbon-bearing waste substances such as, for example, dried sewage sludge or other carbon-bearing waste such as refuse, waste paper, lignite, as well as waste from wood, plastic material, rubber or the like can be introduced (DE-A 29 35 544). In regard to appropriate tests or results however, all that was put forward were assumptions as to the manner in which such substances are to be introduced into the blast furnace. DE-A 41 04 252 also proposes introducing plastic-bearing waste substances into a blast furnace in a fine-grain or dust form by way of the tuyeres, with the introduction of sewage sludge (dust capable of trickle flow) being referred to by way of example. It is expressly emphasized that this process also requires that the substance, which is to be injected, be of a fine-grain nature.